The long term objectives of the research is to provide fast, interference free chemistries for the clinical laboratory using immobilized enzymes and sensors. The specific aim of this proposal is to prove that it is feasible to measure creatinine using immobilized enzymes and sensors in less than two minutes. Because of the specificity of the enzyme creatinase, the assay should be interference free. All fast (less than 3 minutes) current methodologies for measuring creatinine have interference from keto- acids, drugs, and proteins. Because many long term diabetic patients can be ketotic and suffer from kidney dysfunction, an accurate creatinine test is of great importance. The assay will be based on immobilizing creatinine amidohydrolase, and hydrolyzing creatinine to creatine. The sample before and after hydrolysis will be measured by the kinetic Jaffe method. The difference in rates is directly proportional to the creatinine concentration in the sample. This immobilized enzyme/sensor technology could supplant both the common Jaffe chemical method for measuring creatinine and the slow, expensive optical enzymatic procedures, as the standard technique for the clinical laboratory.